Open Access Case Report DOI: 10.7759/cureus.14102 Imaging of Non-ossifying Fibromas: A Case Series Jashmitha Rammanohar 1 , Chen Zhang 1 , Azeem Thahir 2 , Matjia Krkovic 2 1. Medicine, School of Clinical Medicine, University of Cambridge, Cambridge, GBR 2. Trauma and Orthopaedics, Addenbrooke's Hospital, Cambridge University Hospitals National Health Service Foundation Trust, Cambridge, GBR Corresponding author: Jashmitha Rammanohar, [email protected] Abstract Non-ossifying fibromas (NOFs) are common lesions most frequently found in the growing bones of children and adolescents. Although NOFs are benign, their presence as incidental findings often triggers further investigation as they are sometimes mistaken for more sinister bone lesions such as aneurysmal bone cysts. NOFs can also pose an increased risk of pathological fractures. However, there are currently no guidelines on the follow-up of NOFs. We present a case series of five patients from Addenbrooke’s Hospital with NOFs illustrating their morphological features on plain radiographs and highlighting specific characteristics to support clinicians in diagnosing and managing NOFs. Categories: Pediatrics, Radiology, Orthopedics Keywords: non-ossifying fibroma, bone lesion, paediatric orthopedics Introduction Non-ossifying fibromas (NOFs) are common bone lesions, estimated to be present in 20-30% of all four to ten-year-olds [1]. They are characterized by benign growths of osseous and fibrous tissue and most frequently affect the metaphysis of the distal femur and the proximal tibia [2]. Although NOFs are benign, their presence on X-ray imaging often leads to further, usually unnecessary investigations such as MRI, CT, and biopsies. It is thought that certain NOFs increase the risk of pathological fractures in the growing bones of children. However, little progress has been made in understanding which of these lesions are at higher risk. The Ritschl stage has been proposed to classify NOFs based on their natural radiological progression. These stages are based on the appearance of NOFs on plain radiographs. Stage A lesions are lucent with clear margins. Stage B lesions are lucent with a thin sclerotic border while stage C lesions show increasing sclerosis and stage D lesions are completely sclerosed [3]. It has been reported that Ritschl stage B lesions are at higher risk of fractures and thus follow-up has been recommended until stage C is achieved [2]. We present five patients found through the Addenbrooke's Hospital's electronic patient record system (EPIC) who were identified with at least one NOF. We identified the common imaging modalities used to investigate these patients and staged these lesions by Ritschl stage, using the methodology implemented by Blaz et al. [4]. The main outcomes analyzed for this case series were (1) the patient's presentation and clinical features, (2) the imaging modalities used and the assessment of NOFs by Ritschl staging on plain radiograph and, (3) Review began 03/16/2021 assessing the risk of fracture and management of these patients. Review ended 03/22/2021 Published 03/25/2021 © Copyright 2021 Case Presentation Rammanohar et al. This is an open access We analyzed patients based on their demographics, clinical presentation, workup, presence of fracture, article distributed under the terms of the Creative Commons Attribution License management, and clinical outcomes. The age at presentation ranged from 9 to 27 years old with three CC-BY 4.0., which permits unrestricted female and two male patients. None of the patients had a concurrent fracture at the site of the NOF or use, distribution, and reproduction in any required surgery for the management of their NOF. Plain radiographs of these patients were used to stage medium, provided the original author and their NOFs according to the Ritschl stage. One stage A, one stage B, one stage D, and two stage C lesions at source are credited. the time of initial presentation were identified after Ritschl staging. These findings are summarised in Table 1. How to cite this article Rammanohar J, Zhang C, Thahir A, et al. (March 25, 2021) Imaging of Non-ossifying Fibromas: A Case Series. Cureus 13(3): e14102. DOI 10.7759/cureus.14102 Case Age Gender Greatest Length Ritschl Imaging Modality at Time of Follow- Bone Location Number (yrs) (M/F) (cm) Stage Presentation up 1 9 M 3.3 Femur Diaphysis D X-ray and MRI No 2 15 M 6.7 Tibia Metaphysis B X-ray only Yes 3 11 F 3.0 Fibula Diaphysis A X-ray and MRI Yes 4 14 F 2.7 Radius Metaphysis C X-ray and MRI Yes 5 27 F 4.0 Femur Metaphysis C MRI only No TABLE 1: Summary of patients' characteristics. Case 1: A nine-year-old boy presented to the ED with left-sided lower back pain radiating to the groin region. The pain was worse on walking but relieved by sitting and lying down. One café-au-lait spot was noted on the boy’s left arm. Bilateral anteroposterior (AP) and frog-leg lateral radiographs showed no evidence of a slipped upper femoral epiphysis (SUFE) or fracture. Following referral to the pediatric orthopedic clinic, a diagnosis of biomechanical pain was concluded. An incidental finding of a sclerotic lesion of non-aggressive appearance in the left femoral diaphysis was reported on a plain radiograph (Figure 1A). The cortically based lesion measured 3.3 cm in length and had a lentiform shape. At its widest point, the lesion nearly occupied the entire medullary cavity. An MRI scan was requested for further imaging. The T1-weighted MRI showed a discrete sclerotic rim with a distal hyperintense rim (Figure 1B). Despite its thin appearance, the cortex was intact with no periosteal reaction. This was a solitary Ritschl stage D NOF with no concurrent fracture. FIGURE 1: X-ray and MRI images of Case 1. Figure 1A shows a plain radiograph of a completely calcified NOF in keeping with a Ritschl stage D lesion. Figure 1B shows the MRI of the same NOF. NOF: Non-ossifying fibroma. Case 2: A 15-year-old boy presented with a two-month history of left ankle pain possibly related to a sports injury. The ankle was tender to touch on the anterolateral aspect. The foot was externally rotated, and an antalgic gait was noted. A palpable lesion was found on the lateral aspect of the ankle. On imaging, a lesion of 6.7 cm in length was found in the distal diaphysis of the left tibia, a few centimeters above the physis. The lesion occupied the entire width of the diaphysis and was multilobulated with a sclerotic margin, lying against the cortex (Figure 2A). No fracture was noted at the time of presentation. After three years, the NOF was noted to be the same size and in the same location with greater ossifications of the margin (Figure 2B). 2021 Rammanohar et al. Cureus 13(3): e14102. DOI 10.7759/cureus.14102 2 of 7 FIGURE 2: Plain radiographs of Case 2. In Figure 2A, a lucent lesion in the left distal tibia with polycystic borders in keeping with a Ritschl stage B NOF is seen. Figure 2B shows the same lesion three years later. NOF: Non-ossifying fibroma. Case 3: An 11-year-old girl came to the ED with acute onset right anterior knee pain after tripping over while on a walk. A few months later, she was seen in the clinic for recurrent falls and knocking knees. Radiographs showed mild genu valgum. A very small translucent lesion was seen in the lateral cortex of the proximal fibula (Figure 3A). A year later, the genu valgum had improved but the patient complained of pain over the tibial tuberosity and mid patella tendon. On re-imaging, radiographs now showed the same translucent lesion but larger in size and in the same location (Figure 3B). The growth of this lesion warranted a T1- weighted MRI which measured a 10 mm x 8 mm x 30 mm lesion (Figure 3C). With gadolinium contrast, peripheral enhancement was noted with marked thinning of the lateral cortex. The lesion was subcortical and encroached on the medullary cavity. There was minimal surrounding edema without periosteal reaction or cortical destruction. Six months later, the NOF was unchanged and no other abnormalities were noted. 2021 Rammanohar et al. Cureus 13(3): e14102. DOI 10.7759/cureus.14102 3 of 7 FIGURE 3: X-ray and MRI images of Case 3. Figure 3A shows a small lucent lesion in the proximal fibula. Figure 3B shows the growth of the lesion seven months later. This lucent lesion is in keeping with a Ritschl stage A NOF. The MRI with contrast in Figure 3C shows the same lesion as in Figure 3B encroaching the medullary cavity. NOF: Non-ossifying fibroma. Case 4: A 14-year-old girl presented with a red and swollen right distal radius and reduced range of movements after falling from a curb onto an outstretched hand. A plain radiograph of the wrist was ordered to check for any fractures. Incidentally, a well-circumscribed cortically based lucent lesion at the lateral aspect of the right distal radial metaphysis was noted in the absence of a fracture (Figure 4A). An MRI was subsequently performed to investigate this lesion further and confirmed a 5 mm x 8 mm x 27 mm non-aggressive lesion of low T1 and high T2 signal, strongly in keeping with an NOF (Figure 4B). A tiny ganglion was also noted near the palmar aspect of the scapholunate ligament. The patient was discharged to the care of her primary care physician. 2021 Rammanohar et al. Cureus 13(3): e14102. DOI 10.7759/cureus.14102 4 of 7 FIGURE 4: X-ray and MRI images of Case 4.